1. Field of the Invention
The present invention relates to computer data processing and graphics, and in particular, to computational tasks including, but not limited to, volume rendering and image processing operations.
2. Related Art
Three-dimensional arrays of digital data representing spatial volumes arise in many applications. Computed tomography (CT) and magnetic resonance (MR) scanners create a volume by imaging a series of cross-sections, also called slices. Astrophysical, meteorological, and geophysical measurements, and business or economics data also naturally lead to a volume data set. Computer graphics systems use a volume rendering algorithm to display a visualization of a volume. See, R. Drebin, L. Carpenter, and P. Hanrahan, "Volume Rendering," Computer Graphics, Vol. 22, No. 4, (SIGGRAPH '88, Atlanta, Ga.), August 1988, pp. 65-74 (incorporated in its entirety herein by reference); and B. Cabral, N. Cam and J. Foran, "Accelerated Volume Rendering and Tomographic Reconstruction Using Texture Mapping Hardware," Proceedings of ACM/IEEE Symposium on Volume Visualization (IEEE CS Press), pp. 91-98, 1994 (Order No. PR07067, 1995)(incorporated in its entirety herein by reference); and the co-pending, commonly-owned U.S. patent application by B. Cabral and J. Foran, "A System and Method of Performing Tomographic Reconstruction and Volume Rendering Using Texture Mapping," filed Jul. 7, 1995, Appl. Ser. No. 08/499,614 (SGI Ref. No. 15-4-148.00, SKGF Ref. No. 1452.0420000) (incorporated in its entirety herein by reference).
In computer graphics platforms, the re-sampling speed limits fast volume-rendering. For example, one common volume rendering approach uses maximum intensity projection for volume rendering. In one implementation of this type of volume rendering, slices Si are first assumed to be parallel to a viewpoint. For example, as shown in FIG. 1, eight slices S1 to S8 can be used as a volume data set. Slices S1 to S8 each have m bits of grey-scale channel data representing corresponding MR scan cross-section images. For example, grey-scale data can represent pixel intensity ranging from black to white using a single digital value, such as 0 to 256, where 0 represents black and 256 represents white and 1 to 255 represent progressive intermediate shades of grey.
Each slice S1 to S8 is then loaded as a separate one-channel luminance texture (total 8 one-channel textures). The textures for slices S1 to S8 are then drawn on top of each other successively using blending. For example, in a system supporting a graphics application programming language, such as OpenGL.TM. manufactured by Silicon Graphics, Inc., a blending function can be set to draw each slice one on top of the other. Consequently, resampling is performed for each slice in succession and the result is stored in a frame buffer prior to being displayed. Each successive resampling operation which must be performed slows overall volume rendering time.
What is needed is a method, system and computer program product for fast computation that increases resampling and blending speed. The number of successive resampling operations which must be performed needs to be reduced.